A multi-mode device that has performed association and registration with multiple RAT networks, such as cellular and WLAN, can be addressed by these networks independently. A typical implementation of a multi-mode device will require the device to monitor all networks to which the device is registered for incoming data.
Different RATs may provide respective advantages when in communication with the multi-mode device. A cellular RAT may have a low wake-up frequency in idle mode and a wide coverage area. A WLAN RAT may have a higher wake-up frequency in idle mode and a limited coverage area, but may provide higher data rates than cellular RATs and is preferred for applications that benefit from a high data rate. From a power consumption perspective, cellular RATs are generally more efficient for multi-mode devices while in idle mode. However, WLAN RATs are generally more efficient when transmitting at high data rates. In addition, user experience during data activity is generally better over WLAN RATs.
A multi-mode mobile device in simultaneous coverage of two or more RATs may not operate optimally. Each RAT may have one or more advantages over other RATs, such as power consumption, latency, data rate, coverage area, tariffs, reliability, etc. There have been some efforts aimed to reduce power consumption of a multi-mode device by optimizing the interaction between the multi-mode device and a network. For example, a Power-efficient Communication Protocol was proposed (http://www.antd.nist.gov/pubs/Slee-Power-Efficient-icc06.pdf) to turn off the WLAN interface after a multi-mode device enters the idle state, and uses existing paging of a cellular RAT in order to wake up the WLAN interface. Unfortunately, this approach requires coordination between multiple core network elements, including specific signaling and data transfer between network elements, which is difficult and costly to implement.